Description of the life cycle stages

Numerous raw materials are used in the manufacture of displays. In the following, the essential production steps and raw materials utilized for each of the display technologies considered are described and summarized. Detailed illustrations can be found in the chapter on life cycle stages.

Production of a CRT monitor includes manufacture of the two main components, the panel glass and the glass bell; the glass contains a fair amount of lead. The individual luminescent phosphors are then applied to the panel glass and sealed with a protective coating. A pre-assembled shadow mask or aperture grille is then attached. The two glass components are fitted together to form the glass flask or picture tube into whose neck the cathode is then fused. Subsequently, the air is pumped out and the tube is sealed. After manufacture of the tube, other components such as the deflection unit are added in the final assembly (see Fig. 34).

The following section describes the usual steps in the manufacture of an LCD display. One should be aware that various methods can be used, particularly in applying the liquid crystal layer. First, the rear glass plate with TFT layer and the front glass plate and color filters are produced. After that, the ITO layer is sputtered or printed, followed by application of the hard layer and tempering. Then the polyimide (PI) layers are printed and the cured PI layer is rubbed to enable subsequent orientation of the LC molecules. After that spacers are sprayed on, followed by seal deposition and curing and application of external contacts for later wiring. During the subsequent cell assembly, the two glass plates are aligned and assembled to complete a panel. After curing in the hot press oven, the liquid crystal fluid filling is added to the panels and polarizer filters are applied (Crystec Technology Trading GmbH 2003)(see Fig. 35).

The manufacture of a plasma display begins with the fabrication of two glass plates, usually 3 mm thick, which are subsequently cleaned. Metal electrodes are applied in rows to the front plate. The next step is the preparation of the black matrix. The entire front plate is covered with a transparent dielectric ceramic layer, which cures at a temperature of almost 600°C. The front plate is then covered with a thin layer of magnesium oxide (MgO). On the rear plate, electrodes are also applied (in columns/matrix) and likewise coated with a dielectric ceramic layer. After curing of the ceramic layer, a magnesium oxide layer is applied. Subsequently, the so-

called barrier ribs are formed on the parallel electrode surfaces and the phosphors are deposited into the resulting channels. The rear plate is then fired, before the two plates are finally assembled into one panel and fused together. The air is then evacuated from the inner space and replaced by a gas mixture (mostly helium and xenon) at a pressure of about 500 torr (Deschamps 2000)(see Fig. 36).

The manufacture of OLEDs begins with the application of the transparent ITO layer to a glass substrate. In the following steps, all additional organic and metallic layers are then applied by means of thermal evaporation. The organic materials require a temperature of 300-500°C for evaporation, but silver requires a temperature of 1200°C. The layers are applied in a precisely followed series of complex process steps within a vacuum. Subsequently, the front plate is mounted and the entire assembly is sealed air-tight with a form of epoxy resin.

Presently, only one production plant capable of series production of the first OLEDs is in operation, at SK Display Corporation, a joint venture of Kodak and Sanyo (Webelsiep 2003). A prototype of an in-line OLED production system, funded by the Federal Ministry of Education and Research (BMBF), exists at the Fraunhofer IPMS in Dresden (IPMS 2003). The plant consists of eleven process modules, in which 300 x 400 mm samples are coated. The substrates move vertically through the deposition chambers. Up to twelve line sources are available for deposition of the organic layer systems. Additionally, two PVD and inorganic evaporation sources are integrated into each of the electrode deposition systems (see Fig. 37).

The following two illustrations make clear the reduction in manufacturing complexity of the OLED as compared to the LCD (described above).

Fig. 32. Comparison of LCD and OLED (1)

Active matrix plate Fig. 33. Comparison of LCD and OLED (2)

From the diagrams it can be seen that the OLED can be manufactured much more efficiently than the LCD because, e.g., no backlight is in-

volved. This makes it possible to reduce the depth of the screen from 5.5 mm in the LCD to 1.8 mm in the OLED.

An assessment of the materials required for a typical OLED:

• 100 nm organic material

for a 17" display with a viewable area of 918 cm2, this results in an organic materials consumption of ca. 370 mg per display (including waste). The annual production of 1 million 17" displays would require roughly 0.4 t of organic materials.

Table 28. Estimate of typical OLED materials consumption

Contained in the display

Total consumption incl. manufacture

Organic materials

Mg, Ag

12 ^g/cm2 11 mg for 17" 16-20 ^g/cm2 15-18 mg for 17"

100 ^g/cm2 92 mg for 17"

25 ^g/cm2 23 mg for 17" 400 ^g/cm2 370 mg for 17"

ca. 200 ^g/cm2 184 mg for 17"

After production of the rear glass plate of the CNT FED, metal catalysts are applied to the pixel areas of the glass substrate by means of various procedures, including sputtering, lithography, microcontact printing, and ink jet printing. The carefully controlled growth of the CNT on the catalysts takes place in a precisely moderated CVD process at low temperatures (temperatures less than 500°C and lasting only for a few minutes) (NEDO). On the front plate, which also consists of glass, an ITO layer is applied as an anode to the interior face and is then treated with a phosphor layer. Finally, the two plates are combined to form a panel and bonded together (see Fig. 38).

CRADLE-TO-GATE STAGES (Upstieam and Manufacturing)

Japanese electric l'Ic [linked to manufacturing processes (*)btiovv: upstream processes have imbedded electricrty generation inventory data]

Notes.

LPG = liquified petroleum gas HIPS = high impact polystyrene ABS = acrylonitrile butadiene styrene PC = polycarbonate

* Manufacturing stage processes

Invar mfg

PC mfg

ABS mfg

End of Life

U.S. electric grid

(linked to use & EOL processes below: fuel processesand secondary EOL processes have imbedded electricity generation inventory data)

key:

secondary

primary

data

data

CZ3 O O

CRADLE-TO-GATE STAGES (Upstream and Manufacturing)

Japanese electric grid [linked to manufacturing processes (*) below upstream processes have imbedded electricity generation inventory data]

aluminium mfg

Wo res.

PMMA = polyrmethyl methyacrylate PC = polycarbonate PET = polyethylene terphthalate LPG = liquified petroleum gas

fuel oil #2'

LPG'

natural

gas

" Manufacturing stage processes

key:

secondary data

primary data

Plasma monitor assembly

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